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Dropwise condensation heat transfer is significantly higher than filmwise condensation heat transfer due to the absence of the thermal resistance associated with the condensed water film. This study uses electrowetting to enhance coalescence and roll-off of condensed droplets, with the objective of enhancing the condensation rate. Coalescence enhancement is achieved by electric field-driven droplet motion such as translation of droplets, and oscillations of the three-phase line. Experiments are conducted to study early-stage droplet growth dynamics, and steady state condensation under electrowetting fields. Results show that droplet growth and roll-off increases with the voltage and frequency of the applied AC field. AC electric fields are seen to be more effective than DC electric fields. The overall condensation rate depends on the roll-off size of droplets, frequency of roll-off events, and on the interactions of the rolled-off droplets with the remainder of the droplets. All these phenomena can be altered by the applied electric field. An analytical heat transfer model is developed which uses the measured droplet size distribution to estimate the surface heat flux. Overall, this study reports that electric fields can enhance the condensation rate by more than 30 %.
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Batch-Operated Condensed Droplet Polymerization to Understand the Effect of Temperature on the Size Distribution of Polymer Nanodomes
Size-controlled polymer nanodomes (PNDs) benefit a broad cross-section of existing and emerging technologies. Condensed droplet polymerization (CDP) is a vacuum-based synthesis technology that produces PNDs from monomer precursors in a single step. However, the effect of synthesis and processing conditions on the PND size distribution remains elusive. Towards size distribution control, we report the effect of substrate temperature, on which monomer droplets condense, on the size distribution of PNDs. We take a reductionist approach and operate the CDP under batch mode to match the conditions commonly used in condensation research. Notably, despite the rich knowledge base in dropwise condensation, the behavior of nonpolar liquids like a common monomer, i.e., 2-hydroxyethyl methacrylate (HEMA), is not well understood. We bridge that gap by demonstrating that dropwise condensation of HEMA follows a two-stage growth process. Early-stage growth is dominated by drop nucleation and growth, giving rise to relatively uniform sizes with a lognormal distribution, whereas late-stage growth is dominated by the combined effect of drop coalescence and renucleation, leading to a bimodal size distribution. This new framework for understanding the PND size distribution enables an unprecedented population of PNDs. Their controlled size distribution has the potential to enable programmable properties for emergent materials.
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- PAR ID:
- 10483560
- Publisher / Repository:
- Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany
- Date Published:
- Journal Name:
- Organic Materials
- Volume:
- 5
- Issue:
- 02
- ISSN:
- 2625-1825
- Page Range / eLocation ID:
- 148 to 157
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1055/s-0043-1761311
